This invention relates to optoelectronic devices and more particularly to a light emitting device fabricated from an indirect bandgap semiconductor material and to a method of generating light.
Avalanche electroluminescent light emission in single crystal indirect bandgap semiconductors (e.g. silicon) is generated by the interaction between mobile hot carriers (e.g. recombination of electrons and holes) and lattice phonons in reverse biased pn junctions.
In conventional reversed biased n+p junctions in silicon devices, carriers experience impact ionization over a short distance only in the depletion region. A low electric field at the end of the p side remote from the junction means that hot or energetic carriers are only present at the n+ side of the depletion region and that holes leaving the depletion region at the opposite side thereof will be low energy carriers. If the carrier recombination rate is proportional to the product p*n of the hole p and the electron n concentrations, carrier recombination will occur in a short region of the depletion region only. These features and parameters, together with the fact that in the known devices a major part of the sidewalls of the depletion region is bordered by bulk semiconductor material, contribute to an internal quantum efficiency, which is not satisfactory.